The Sun, the head of the solar family, is the star at the center of the Solar System. It is an almost perfectly spherical ball of gases with internal motion that generates a magnetic field. The Sun is composed mainly of hydrogen (73%) and helium (25%). It is the most important source of energy for life on Earth. The Sun appears to be far bigger and brighter than any other stars, as it is nearer to the Earth than all the other stars. It is about 13 billion times brighter than the next brightest star, Sirius. The diameter of the Sun is 100 times more than that of the Earth and its mass is about 330,000 times that of Earth.
The core of the Sun extends from the center to about 20-25% of the solar radius and the temperature at the core or centre of the Sun is around 1.4 million ºC. Through fusion, the Sun produces an appreciable amount of thermal energy only from its core region.
The atmosphere of the sun is composed of several layers, mainly the Photosphere, the Chromosphere and the Corona.
The visible yellow face of the Sun is called ‘Photosphere’ or the sphere of light. It is about 300 miles or 500 kilometers thick. Here the temperature is about 6000ºC. Sometimes dark patches are seen in the Photosphere. Known as ‘Sunspots’, they are the darker and cooler spots, where the average temperature is about 4500ºC. The Photosphere is the source of solar flares, the tongues of fire that extend hundreds of thousands of miles above the sun's surface. Solar flares produce bursts of X-rays, ultraviolet radiation, electromagnetic radiation and radio waves.
Surrounding the Photosphere is the ‘Chromosphere’, which emits reddish or pinkish glow as super-heated hydrogen burns off. However, the red rim can only be seen during a total solar eclipse. At other times, light from the Chromosphere is usually too weak to be seen against the brighter photosphere.
The third layer of the sun's atmosphere is the corona, which also can only be seen during a total solar eclipse. It appears as white streamers of ionized gas that flow outward into space. Temperatures in the sun's Corona can get as high as two million degrees Celsius.